U.S. Pat. Nos. 4,978,251, 4,952,099, 4,992,006 and 5,853,266, disclose fluidising units of the type comprising a supply duct which is arranged to be fed with liquid under pressure, and a discharge duct within the supply duct, and projecting beyond the outlet of the supply duct.
A particular disadvantage of the fluidising units described in the above mentioned patents is that the discharge duct is always within the slurry duct. This can lead to a requirement to have large units and in particular large nozzles in pressure vessels etc. As the fluidising units may require inspection and/or maintenance the units in practice are normally designed to be removable, through nozzles or manways. The larger the dimension of the fluidising unit the more demanding the design of the pressure vessel becomes.
It has also been observed in practice that a large fluidising unit installed inside a pressure vessel can cause a hold-up of material on its top or within the annulus, created by the fluidising unit and its pressure vessel, by the formation of a bridge of solids.